The principles of the invention are particularly applicable to pay TV systems wherein TV programs are transmitted from a central station to a plurality of remote stations, and it is desired to determine in simple fashion whether a subscriber has selected and received a program, and, if this occurs, then the system automatically bills the subscriber for the program. Systems are known for performing this function; however, such systems are either excessively complex and expensive and do not operate with suitable simplicity, or they are not sufficiently automatic and require excessive human participation.